1986 xr600 dual carb rebuild

Recently purchased a rebuild kit for my 1986 xr600 and it came with #118 and #115 mains and #45 slow jets. I've read many posts about guys running #122 jets. What gives? Just don't want to be too lean. Bike is all stock and will be used mostly trail riding in Montana.

118s might be better for higher altitude. 122s were stock in some years and can't hurt anything but gas mileage. Generally 1 or 2 sizes bigger pilot jets seem to help starting and low speed transition though. Guideline I've  been taught many decades back was if your air screw is less than 3/4 turn the pilots too small, more than 1 1/2 your too large. Just the opposite for a fuel screw. I don't make any claims of being a jetting guru however and often consult other threads here to get all the opinions possible. When I get easy starting, clean acceleration and a brown plug I'm done. I don't need every last tenth of a horse power, that's what a 650 is for.

That jetting is very close for XR carbs at sea level from my experience.  As VR suggested you may find it needs to be a little leaner for altitude.  I am running a 42 pilot jet which greatly improved hot restart.  For higher altitude one notch leaner would be desired on my bike as it gets harder starting hot the higher I ride. 

I run a 122/110 for the summer normally at 0-4000 feet, and that is equivalent to 118/115.  I find a richer primary give me a more linear throttle response.  Take the sum of both jets and divide by two in order to get your overall jetting.  122+110=232 /2=116.   118+115=233 /2+116.5.  They run best from my experience at 116 to 119 overall main size depending on altitude and temp.

Winter in Montana you might want a 122 primary with your 115 secondary.

Stock jetting for an 87 xr600r is 122, 122, 45. making122's common.

You didn't mention if the exhaust and air filter are stock or aftermarket. This can have a considerable impact on jetting.

Mine is an 86, everything is stock except for a k&n style air filter element.

Mine is an 86, everything is stock except for a k&n style air filter element.

I think the above posts should get you in the ballpark. I tend to jet a little on the rich side to keep temps down so if most of your riding is in the 2000' range I would probably start with 120/118 or 122/120 in the mains.

For the pilot, do as posted above and size according to mixture screw.

Just my 2 cents but I wouldn't run a k&n filter on anything used in the dirt. A UNI is a much better filter.

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